1. Field of the Invention
The present invention relates to a process for preparing catalyst composition for the synthesis of carbon nanotube with high yields using the spray pyrolysis method. More particularly, this invention relates to a process for preparing catalyst composition for the synthesis of carbon nanotube comprising the steps of i) dissolving multi-component metal precursors of catalyst composition in de-ionized water; ii) spraying obtained catalytic metal precursor solution into the high temperature reactor by gas atomization method; iii) forming the catalyst composition powder by pyrolysis of gas atomized material; and iv) obtaining the catalyst composition powder, wherein said catalyst composition comprises i) main catalyst selected from Fe or Co, ii) Al, iii) optional co-catalyst at least one selected from Ni, Cu, Sn, Mo, Cr, Mn, V, W, Ti, Si, Zr or Y, iv) inactive support of Mg. Further, the catalyst composition prepared by this invention has a very low apparent density of 0.01˜0.50 g/ml as well as the catalyst composition affords high production yield (1,000˜4,800%) of carbon nanotube.
2. Description of Prior Art
Carbon nanotube has a hexagonal honey comb shape in which one carbon atom is bonded with 3 adjacent carbon atoms. Further, the graphite plane is rolled in a round shape having nano size diameter. Specific physical properties are shown according to the size and shape of carbon nanotube. The weight of carbon nanotube is comparatively light due to its hollow structure. Further, the electrical conductivity is as good as that of copper as well as the thermal conductivity is as good as that of diamond. Of course, the tensile strength is not less than that of iron. Carbon nonotube can be classified as single walled carbon nanotube, multi-walled carbon nanotube and rope carbon nanotube depending on its rolled shape.
Such carbon nanotube can be generally manufactured by an arc-discharge method, a laser vaporization method, a plasma enhanced chemical vapor deposition method, a thermal chemical vapor deposition method, a vapor phase growth method or a electrolysis method. Among them, a thermal chemical vapor deposition method has been preferably used, because the growth of carbon nanotube can be made by the direct reaction between carbon source gas and metal catalyst without using the substrate. Further, high purity of carbon nanotube can be economically manufactured in a large amount according to a thermal chemical vapor deposition method.
In a thermal chemical vapor deposition method, the metal catalyst is necessarily required. Among the metals, Ni, Co, or Fe has been commonly used. Each particle of metal catalysts can act as seed for the formation of carbon nanotube. Therefore, the metal catalyst has been required to be formed as nano size particle. Of course, many researches for developing metal catalyst have been tried.
As a preparation method of metal catalyst reported until now, following preparation methods have been disclosed. First, the method comprising i) preparing the solution containing catalytic metals and support, ii) co-precipitating the catalyst composition by adjusting pH, temperature and/or amount of ingredients, and iii) heat treating the precipitates under air or other gas atmosphere has been disclosed. Second, the method by drying or evaporating the suspension containing catalytic metal and fine grain support has been disclosed. Third, the method comprising i) ionizing the metal by mixing catalytic metal salt with cation particle support such as zeolite, and ii) reducing the ionized metal into metal particle by hydrogen or other reducing agent at high temperature has been disclosed. Finally, the method by calcinating catalytic metal with solid oxide support material, such as, magnesia, alumina and/or silica has been disclosed.
According to a catalytic chemical vapor deposition method, the metal catalytic components are slowly consumed in the process of synthesizing carbon nanotube. This consumption of metal catalytic components is caused by the inactivation of metal components by encapping, where carbon atoms encapsulate metal catalytic particle. Generally, re-activation of inactivated catalytic metal is neither possible, nor economical. In some cases, only few grams of carbon nanotube can be obtained using 1 gram of a metal catalyst composition including metal catalyst and support material. Therefore, the development of a high yield metal catalyst composition and of synthetic conditions has been required in order to produce the carbon nanotube in a commercially available scale
Following technologies have been reported in patent disclosures or references until now.
In U.S. Pat. No. 6,696,387 by Hyperion Catalysis International Inc., the catalyst composition comprising i) Fe as main catalyst, ii) alumina and/or magnesia particle as catalyst support and iii) at least one optional co-catalyst selected from V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt or the lanthanides has been disclosed. However, it is hard to obtain a precise multi-walled carbon nanotube with a high catalytic yield using this catalyst composition, because the uniform dispersion between metal catalyst and support material cannot be accomplished due to the use of alumina and/or magnesia support material.
In Korean early patent publication No. 10-2007-82141 ‘Process for preparing catalyst for the synthesis of carbon nanotube’, a process for preparing catalyst for the synthesis of carbon nanotube comprising the steps of i) preparing transition metal precursor solution after dissolving transition metal precursor with solvent; ii) absorbing the transition metal precursor into the surface of solid oxide support; and iii) fixing the transition metal into the surface of support by spray pyrolysis of obtained solution in previous step has been disclosed. However, the use of solid oxide support selected from zeolite, silica, magnesia, zirconia and/or mixture of them inhibits uniform dispersion of metal catalyst composition. Further, the solid oxide support causes the closing of spray nozzle in the course of spray pyrolysis. Therefore, this preparation method has a handicap of commercialization.
In Korean early patent publication No. 10-2007-110739 ‘Process for preparing catalyst for the synthesis of carbon nanotube and an apparatus thereof’, a process for preparing catalyst for the synthesis of carbon nanotube comprising the steps of i) preparing metal catalyst solution after dissolving metal precursor and support material precursor with solvent; ii) making a mist phase of metal catalyst solution by ultrasonic spray method; iii) forming the catalyst-support conjugate powder by pyrolysis of obtained mist phase of metal catalyst solution; and iv) obtaining the catalyst support conjugate powder has been disclosed. However, the use of ultrasonic spray causes partly education of metal precursor as well as change of metal ratio in catalyst solution. Further, the educated material causes the closing of spray nozzle in the course of spray pyrolysis. Therefore, this preparation method also has a handicap of commercialization.
In Korean patent No. 10-913369, ‘Apparatus for manufacturing catalyst for carbon nanotube using spray pyrolysis method and method for preparing catalyst’ a process for preparing catalyst for the synthesis of carbon nanotube comprising the steps of i) adding Fe, Ni, Co or its precursor; Al or its precursor; Mg or its precursor; and Mo or its precursor respectively into ammonia water; ii) mixing the said components in ammonia water; iii) drying and calcinating the catalyst components at high temperature after spraying the mixed component in a liquid state; and iv) obtaining the dried catalyst powder has been disclosed.
However, this preparation method of catalyst for carbon nanotube has following handicaps; i) forming the precipitate in the course of preparing multi component catalyst solution by mixing catalyst metal and ammonia water due to the reaction between catalyst metal precursors and ammonia; and ii) closing the spray nozzle or hindering the spray of nozzle by such precipitate.
Therefore, the present invention has been developed to overcome above problems in the course of preparing catalyst for carbon nanotube according to spray pyrolysis method. In other words, this invention has prevented following problems of spray pyrolysis method; i) the difficulty of uniform dispersion of metal catalyst onto a support material when solid oxide support powder is used and the closing of spray nozzle by support powder in the course of spray pyrolysis method; ii) the closing or hindering the spray nozzle by precipitate which is formed when ammonia water is used as a solvent.
Therefore, the inventors of present application have made the uniform dispersion of metal catalyst using an aqueous solution in which all components of metal catalyst are completely dissolved without any raw materials which result in precipitation and support powder. Further, the present preparation method of catalyst for the synthesis of carbon nanotube has accomplished the mass production of catalyst composition in a high yield in economical way, by solving the conventional problems of spray pyrolysis method, for example, closing or hindering the spray nozzle, additional apparatus or processing step for preparing catalyst, such as ultrasonic spray.
Further, the catalyst composition for the synthesis of carbon nanotube according to present spray pyrolysis method can afford a very low apparent density of 0.01˜0.50 g/ml as well as a high production yield (1,000˜1,800%) of carbon nanotube.